In a three-phase voltage system, the three-phase voltage or current can become unbalanced. In such a case, it is desirable to balance the three-phase voltage or current. One way to achieve this is through the use of a static synchronous compensator (STATCOM), which supplies a signal to the three-phase power system that balances the three-phase voltage or current.
A STATCOM is a regulating device used on alternating current electricity transmission networks. It is based on a power electronics voltage-source converter and can act as either a source or a sink of reactive AC power to an electricity network. If connected to a source of power it can also provide active AC power.
However, when a conventional system balances voltages or currents in a three-phase power system, the STATCOM compensates for unbalanced magnitudes by adjusting the magnitudes of the voltages or currents. The phases of the three-phase power system (i.e., the phases of an A voltage or current, a B voltage or current, and a C voltage or current) are always kept 120 degrees apart. In other words, the A voltage or current will always be 120° separated from the B voltage or current; the B voltage or current will always be 120° separated from the C voltage or current; and the A voltage or current will always be 120° separated from the C voltage or current.
It would therefore be advantageous to balance a three-phase power system by changing the phase relationship between the three-phase voltages or currents in addition to or instead of changing the magnitudes of these signals.